Ion-mediated nucleation as an important global source of tropospheric aerosols
1Atmospheric Sciences Research Center, State University of New York, 251 Fuller Road, Albany, New York 12203, USA
2NZC/LAPC, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
3Department of Atmospheric and Oceanic Sciences, University of California, 405 Hilgard Ave, Los Angeles, California 90095, USA
Abstract. Aerosol nucleation events have been observed at a variety of locations worldwide, and may have significant climatic and health implications. While ions have long been suggested as favorable nucleation embryos, their significance as a global source of particles has remained uncertain. Here, an ion-mediated nucleation (IMN) mechanism, which incorporates new thermodynamic data and physical algorithms, has been integrated into a global chemical transport model (GEOS-Chem) to study ion mediated particle formation in the global troposphere. The simulated annual mean results have been compared to a comprehensive set of data relevant to new particle formation around the globe. We show that predicted annual spatial patterns of particle nucleation rates agree reasonably well with land-, ship-, and aircraft-based observations. Our simulations show that, globally, IMN in the boundary layer is largely confined to two broad latitude belts: one in the northern hemisphere (~20° N–70° N), and one in the southern hemisphere (~30° S–90° S). In the middle latitude boundary layer over continentals, the annual mean IMN rates are generally above 104 cm−3day−1, with some hot spots reaching 105 cm−3day−1. Zonally-averaged vertical distribution of IMN rates indicates that IMN is significant in the tropical upper troposphere, whole middle latitude troposphere, and over Antarctica. The ratio of particle number annual source strength due to IMN to those associated with primary particle emission suggests that IMN contribution is important. Further research is needed to reduce modeling uncertainties and understand the contribution of nucleated particles to the abundance of cloud condensation nuclei.